1. Field of the Invention
This specification relates to a superconducting rotating electrical machine and a manufacturing method for a high temperature superconducting film thereof, and particularly, to a superconducting rotating electrical machine, capable of preventing deformation of components and improving cooling efficiency, and a manufacturing method for a high temperature superconducting film thereof.
2. Background of the Invention
As widely known, a rotating electrical machine may be used exclusively as a generator for converting mechanical energy into electrical energy or a motor for converting electrical energy into mechanical energy or used as combination of both the generator and the motor.
In general, the rotating electrical machine may include a stator and a rotor rotatable with respect to the stator.
A so-called superconducting rotating electrical machine using superconducting wires has been introduced. The machine may remarkably reduce a loss, compared with a normal conducting rotating electrical machine using copper wires.
As compared with the normal conducting rotating electrical machine, the superconducting rotating electrical machine, as well known, may have a remarkably increased capacity when having the same size, and have a remarkably reduced size when having the same capacity.
FIG. 1 is a side view of a rotor for a superconducting rotating electrical machine according to the related art, and FIG. 3 is a sectional view showing main parts of FIG. 1.
As shown in FIGS. 1 and 2, a superconducting rotating electrical machine may include a stator (not shown), and a rotor 10 disposed to be rotatable with respect to the stator.
The rotor 10 may include a rotary shaft 20, and a rotor winding 30 disposed on a circumference of the rotary shaft 20.
The rotor winding 30 may include a superconducting wire as a conducting wire.
The rotor winding 30, for example, may be configured by winding the superconducting wire in a circumferential direction.
The rotor winding 30 may have a so-called racetrack shape or oval shape.
The rotor winding 30 may be provided in plurality.
The rotary shaft 20 may include a mounting portion 25 formed on a circumference thereof such that the rotor winding 30 is mounted thereon.
A rotor winding support cover 40 for supporting the rotor winding 30 may be detachably coupled to the mounting portion 20.
The rotary shaft 20 may be provided therein with a refrigerant storing space 22. This may allow the rotor winding 30 to be cooled.
The rotor 10 may include an enclosure 50 defining an accommodating space therein.
The inside of the enclosure 50 may be maintained in a vacuum state.
The rotor winding 30 and a part of the rotary shaft 20 may be accommodated within the enclosure 50.
The superconducting rotating electrical machine according to the related art has the so-called racetrack-shaped rotor winding 30 that a superconducting wire long in length is wound in a circumferential direction and pressed to have an extended length in one direction. With the configuration, upon constituting an intermediate capacity device and/or a large capacity device, which have a relatively larger capacity than a small capacity device, a linear section of the rotor winding 30 may be deformed due to being bent (drooped) by its own weight.
In addition, the rotor winding 30 is disposed on an outer surface of the rotary shaft 20. A refrigerant is supplied into the rotary shaft 20 to cool the rotor winding 30 by heat conduction using the rotary shaft 20 as an intermediate. This may cause the rotor winding 30 to be insufficiently cooled (i.e., lowering of cooling efficiency).
In the meantime, a superconductor may allow a large quantity of current to flow without loss. The superconductor refers to a material which is used to make powerful magnets so as to be applied to various fields, such as a magnetic levitation train, a magnetic resonance image (MRI) scanner and the like. The superconductor exhibits a specific magnetic property which is not found in the conventional metals or conductors. Accordingly, the use of the superconductor allows for developing sensors and electronic devices having ultra sensitivities, super high speeds and super high efficiencies which cannot be implemented by the related art devices.
Among those superconductors, a high temperature superconductor exhibits superconducting properties at temperature higher than 77K, which is the boiling point of liquid nitrogen. Therefore, as compared to a low temperature superconductor, it has the advantage in low costs in the aspect of using the liquid nitrogen as a refrigerant.
The high temperature superconductor exists in the form of an oxide. This makes it easy for cracks to be generated on the superconductor due to the lack of ductility. Hence, a high temperature superconducting film which the high temperature superconductor is deposited on a metallic substrate having high malleability or ductility in the form of a thin film may overcome the problem, and have properties superior to general metallic wires. This thusly leads to many studies and development thereof.
FIG. 3 shows a general high temperature superconducting film. As shown in FIG. 3, a high temperature superconducting film 70 has a structure of laminating a buffer layer 72 on a metal substrate 71, and laminating a superconducting layer 73 on the buffer layer 72.
The buffer layer 72 is employed to deposit a ceramic superconducting layer on the metallic substrate, and is a multi-layered oxide layer having a layered structure. The oxide layer is laminated by being deposited on the metallic substrate.
A cap layer 74 and a stabilizer layer 75 are located on the superconducting layer 73. The cap layer 74 is laminated by depositing a metal layer such as silver (Ag) or the like. The stabilizer layer 75 is formed of a metal different from the superconducting layer 73, and serves to protect the superconducting film by allowing a current higher than a threshold current to flow to the stabilizer when the current flows on the superconductor. Also, another stabilizer layer 76 may also be disposed beneath the metallic substrate. FIG. 3 shows a stabilizer layer made of copper (Cu).
Referring to FIG. 3, the high temperature superconducting film has the multi-layered structure. Here, the superconducting layer 73 is formed in the shape of the ceramic thin film which has no elasticity. Consequently, in view of its properties, cracks are easily generated when a mechanical stress is applied thereto.
In particular, cracks are very likely to be generated on the superconducting layer deposited on the metallic substrate due to bending of the metallic substrate which inevitably occurs during processing on the metallic substrate. In the current structure of the high temperature superconducting film, the metallic substrate is the thickest, accordingly, the mechanical stress due to the bending of the metallic substrate is transferred directly to the superconducting layer.
This results in degradation of a current carrying capability of the superconducting layer which allows a high current to flow within a narrow area.